Increasing evidence suggests that the three homologous members of steroid receptor co-activator (SRC) family (SRC-1, SRC-2, and SRC-3) play key roles in enhancing cell proliferation in various human cancers, such as breast, prostate, and hepatocellular carcinoma. However, the function of SRC-3 in osteosarcoma remains largely unexplored. In the current study, we found that SRC-3, but not SRC-1 and SRC-2, was dramatically up-regulated in human osteosarcoma tissues, compared with adjacent normal tissues. To explore the functions of SRC-3 in osteosarcoma, in vitro studies were performed in MG63 and U2OS cells. SRC-3 overexpression promoted osteosarcoma cell proliferation, whereas knockdown of SRC-3 inhibits its proliferation. In support of these findings, we further demonstrated that SRC-3 up-regulated FoxM1 expression through co-activation of C/EBPγ. Together our results show that SRC-3 drives osteosarcoma progression and imply it as a therapeutic target to abrogate osteosarcoma.